1. Field of the Invention
The present invention generally relates to an air conditioning system for buildings and, more particularly, to an air conditioning system which does not employ passages for water, typically used as a thermal medium, at the locations at which air conditioners are installed and which, moreover, permits the air conditioning equipment, especially the refrigerator, to function effectively with a relatively small capacity.
2. Description of the Related Art
Generally, in an air conditioning system in a building, water is used as a thermal medium for facilitating thermal conveyance between the thermal source equipment and the individual air conditioners. Such use of water, however, has presented a problem of water leakage from an air conditioner. Recently, therefore, for air conditioning systems for buildings, introduction of a volatile substance, such as freon, as a thermal medium to be passed directly between the thermal source equipment and the respective heat exchangers of the air conditioners, is being considered to reduce the problem of liquid leakage by virtue of the volatility of the substance.
Such a system using a volatile thermal medium comprises, for both cooling and warming, an outdoor unit which may be placed on the roof of a building and a plurality of indoor units at the air-conditioned locations, said outdoor unit being thermal source equipment including, for example, a refrigerator which also functions as a heat pump, and each of said indoor units being an air conditioner and a thermal medium conduit connecting the outdoor unit and the indoor unit.
An air conditioning system for a building using a volatile thermal medium and structurally designed as mentioned above is based on a direct expansion method according to which the thermal medium liquified by the condenser in the outdoor unit is supplied through the thermal medium conduit directly to the vaporizer in the indoor unit. In this system, the ice machine oil used in the compressor in the outdoor unit partly mixes in the form of mist into the thermal medium and circulates through said conduit. It is necessary for this ice machine oil, carried by the flow of the thermal medium to the indoor unit, to be recovered and returned to the compressor in the outdoor unit. This necessity imposes various restrictions upon the operation of the air conditioning system.
For example, whereas it is desirable that the variation of the air conditioning load at the air-conditioned location be met by the adjustment of the flow rate of the thermal medium supplied to the indoor unit, the conveyance of the ice machine oil for recovery requires the flow rate of the vapor in the thermal medium conduit to be maintained at approximately 6 m/sec. or more. There is a limit to throttling because of the need to maintain an adequate vapor flow. With normal throttling thus being unacceptable for the adjustment of the flow rate of the thermal medium, the only alternative means for controlling the output, available to indoor operators if the variation of the load necessitates it, is to open and close the throttle at short intervals repeatedly more or less simultaneously with turning on and off the fans in the individual air conditioners at short intervals. This method of control is in no way desirable.
The need to recover the ice machine oil also sets a strict limit to the number of indoor units that can be connected to one outdoor unit. In fact, the number of indoor units is limited to two or three for one outdoor unit.
The thermal source equipment, which is in fact a refrigerator, is required to have a relatively large capacity because of the need to cope with peaks of the load. Another factor which requires the capacity to be large is the fact that the thermal medium is circulated under a pressure applied by the compressor in said refrigerator.